Composite alloy bonding wire and manufacturing method thereof

ABSTRACT

A manufacturing method for a composite alloy bonding wire and products thereof. A primary material of Ag is melted in a vacuum melting furnace, and then a secondary metal material of Pd is added into the vacuum melting furnace and is co-melted with the primary material to obtain an Ag—Pd alloy solution. The obtained Ag—Pd alloy solution is drawn to obtain an Ag—Pd alloy wire. The Ag—Pd alloy wire is then drawn to obtain an Ag—Pd alloy bonding wire with a predetermined diameter.

RELATED APPLICATIONS

This application is a continuation-in-part (CIP) application of U.S. patent application Ser. No. 12/408,952, filed on Mar. 23, 2009.

A co-pending application Ser. No. 12/408,987, filed on Mar. 23, 2009 and its divisional application Ser. No. 12/869,854, filed on Aug. 27, 2010, both have received the notice of allowance and will be patented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a bonding wire used as a packaging wire, in particular, to a bonding wire used in the semiconductor packaging process.

2. Description of Related Art

In semiconductor device packaging processes for IC, LED, SAW, a wire bonding process is often performed to electrically connect the chip to the substrate by a bonding wire which is used as a signal and electrical current transmitting medium between the chip and the substrate.

The primary characteristics of the bonding wire, such as the breaking load, elongation, loop, melting point, and bondability with IC chips depend on the materials of the bonding wire. The performance of the packaged semiconductor device is influenced by the characteristics of the bonding wire. According to different types of chip and substrate, the adapted bonding wire has different specification.

The conventional bonding wires are usually made of pure Au material. Pure Au bonding wire has better physical properties, such as elongation and electrical conductivity. However, pure Au bonding wire inevitably leads to a high cost.

Therefore, the subject of the present invention is to solve the above mentioned problem to provide a low cost bonding wire with performance comparable to pure Au bonding wire.

German patent no. DE 3122996 “Silver-palladium-magnesium aluminium alloy for internally oxidized electrical contacts, e.g. spring contacts” is related to an alloy used for electrical breaker and sliding contacts, e.g. in relays, switches and potentiometers. The alloy has the composition (by wt.) of 5-30% Pd, 0.1-0.5% Mg, 0.01-0.5% Al and balance Ag, which is not suitable for making as a bonding wire used for IC, LED, SAW because of the following reasons.

1. When wt. % of Pd is more than 10%, the hardness of the wire will be larger than 150-200 kp/mm2. In comparison, the hardness of the bonding wire is normal 60-90 kp/mm2. That is, the wire made by the alloy of DE 3122996 may not be able to be drawn with a diameter as or less than 0.0175 mm (0.7 mil), and a soldering process may not be performed because it may cause cracking or catering to the IC or LED due to the hardness of the wire.

2. Adding Mg will increase the wear resistance and hardness of the alloy. After adding Mg, an oxidation process has to be performed to obtain MgO particles in the alloy. However, MgO will make the alloy become hard and brittle to be used as a bonding wire for IC and LED. Besides, MgO will increase the resistance of the alloy and decrease the conductivity of the alloy. That is also not good for the alloy to be as a bonding wire.

3. Adding Al will decrease the elongation of the alloy and increase the resistance of the alloy. In addition, adding Al in Ag will produce various configurations of Ag and Al compound in the alloy. These are negative for the alloy to be as the bonding wire.

4. The resistance of the alloy of DE 3122996 is about 0.08-0.16 ohm, mm2/m which is 160-170 times of 0.00023-0.00050 ohm, mm2/m for a general resistance of a bonding wire. The higher the resistance of the bonding wire is, the lower the conductivity will be. The bonding wire with high resistance will reduce the transmission speed and the lifespan of the IC or LED.

SUMMARY OF THE INVENTION

The present invention is to provide a low cost composite alloy bonding wire made of silver (Ag) and palladium (Pd) and excluding magnesium (Mg) and aluminium (Al), capable of having performance as good as a pure Au bonding wire.

Accordingly, a manufacturing method for a composite alloy bonding wire is disclosed. A primary metal material of Ag is melted in a vacuum melting furnace, and then a secondary metal material of Pd is added into the vacuum melting furnace and is co-melted with the primary metal material of Ag to obtain an Ag—Pd alloy solution. The obtained Ag—Pd alloy solution is then cast and drawn to obtain an Ag—Pd alloy wire. Finally, the obtained Ag—Pd alloy wire is then drawn to obtain an Ag—Pd alloy bonding wire with a predetermined diameter.

Besides, a composite alloy bonding wire made by the abovementioned manufacturing method is provided. The composite alloy bonding wire includes 90.00˜99.99 wt. % Ag and 0.01˜10.00 wt. % but no more than 10.00 wt. % Pd.

The composite alloy bonding wire made of silver and Palladium has performance as good as a pure Au bonding wire and a lower manufacturing cost.

BRIEF DESCRIPTION OF DRAWING

The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a flow chart for manufacturing composite alloy bonding wire of the present invention; and

FIG. 2 shows detailed sub-steps in the flow chart of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

In cooperation with attached drawings, the technical contents and detailed description of the present invention are described thereinafter according to a preferable embodiment, being not used to limit its executing scope. Any equivalent variation and modification made according to appended claims is all covered by the claims claimed by the present invention.

Pure Ag has good characteristics as compared to Au or Cu (See below Table 1). However, Ag could not be used as a bonding wire as Au or Cu because during the process of ball bonding, an interfacial reaction will occur between Ag and Al which is in the Al pad formed on a chip to produce the intermetallic compounds such as Ag₂Al, AgAl₄ and Au₅Al₂ which have the hard and brittle characteristics. Meanwhile, the difference between the diffusion rates of Ag and Al is so significant, so Kirkendall voids will be created. As a result, high electrical resistance or open circuits, weak bond adherence or brittle bond heels will be created. The whole integrated circuit should lose its function.

TABLE 1 Iterm Unit Gold Silver Copper Palladium Atomic Symbol Au Ag Cu Pd Atomic Number 79 47 29 46 Melting Point ° C. 1064.4 961.9 1083 1554 Boiling Point ° C. 3080 2212 2567 3140 Density, 20° C. g/cm³ 19.3 10.5 8.96 12.0 Resistivity, 20° C. μΩcm 2.3 1.63 1.69 10.8 Thermal Conductivity W/mK 316 429 401 71.8 Specific Heat J/Kg K 130 234 386 244 Hardness Mohs — 2.5 2.5 3.0 4.75 Hardness Vickers MN/m² 215 215 369 461 Hardness

Nevertheless, Ag should be used as a base metal because of its density, hardness, electrical conductivity, thermal conductivity and the cost. The density of Ag is 10.5 g/cm3, while it is 54.4% of Au. It is light enough to meet the weight requirement of the electronic products. In addition, comparing the hardness of Ag, Au, Cu and Pd, the order is Pd, Cu, Ag and Au from high hardness to low hardness. Under either Mohs or Vickers hardness examination, the harness of Ag is the closest to that of Au. The hardness is critical to IC, LED and SAW because if the material of packaging wire is too hard, it is easy to break or go through the IC chips and destroy the IC, LED or SAW package.

Comparing the electrical resistance of Ag, Au, Cu and Pd, the order is Pd, Au, Cu, Ag from high resistance to low resistance. Ag has the lowest resistance and has the best conductivity. Therefore, the alloy using Ag as a base metal is a good conductor, which is important to IC, LED and SAW.

Comparing the thermal conductivity of Ag, Au, Cu and Pd, the order is Ag, Cu, Au and Pd from high to low. Thermal conductivity of Ag is the biggest and it means Ag has the best cooling capacity, which is important to IC, LED and SAW.

Ag with the purity higher than 99.99% is easy to be broken because its hardness is low during the wire drawing process. As a result, during wire bonding process, partial wire arc may collapse because of the soft material, which may cause short circuit between the wire and cause IC, LED and SAW unable to use.

If pure Pd is used to be the base of the packaging wire, it is not practical because of the hardness, electrical resistance and high cost. Therefore, when Ag is used as the basic material for the alloy, other elements must be added to change the property of Ag. In the present application, the alloy includes Pd and excludes Mg and Al. The advantages of adding Pd are (1) to increase the oxidation resistant effect; (2) to increase the oxidation resistance; (3) to decrease the diffusion rate between Ag and Al, thus to avoid the cracking of the intermetallic compounds and the creation of Kirkendall Voiding.

Refer to FIG. 1 and FIG. 2, which respectively are a flow chart for manufacturing composite alloy bonding wire of the present invention and a drawing showing detailed sub-steps in the flow chart of FIG. 1.

Step 100, a primary material of Ag is provided.

Step 102, the primary material is melted in a vacuum melting furnace (step 102 a). Specific amount of a secondary metal material of Pd is added into the vacuum melting furnace (step 102 b), and co-melted with the primary material in the vacuum melting furnace to obtain an Ag—Pd alloy solution (step 102 c). The Ag—Pd alloy solution consists of 90.00˜99.99 wt. % Ag and 0.01˜10.00 wt. % but no more than 10.00 wt. % Pd.

Subsequently, continuous casting and drawing processes are performed on the Ag—Pd alloy solution to obtain an Ag—Pd alloy wire with diameter of 4-8 mm (step 102 d). The Ag—Pd alloy wire is rewired by a reeling machine (step 102 e) and then composition analysis (102 f) is performed on the Ag—Pd alloy wire to check if the obtained composition meets the requirement.

Step 104, a drawing process is performed on the Ag—Pd alloy wire; the obtained Ag—Pd alloy wire with a diameter of 4-8 mm is drawn by a first thick drawing machine to obtain an Ag—Pd alloy wire with a diameter of 3 mm or smaller than 3 mm (step 104 a). The Ag—Pd alloy wire with a diameter of 3 mm or smaller than 3 mm is drawn by a second thick drawing machine to obtain an Ag—Pd alloy wire with a predetermined diameter of 1 mm or smaller than 1 mm (step 104 b). The Ag—Pd alloy wire with diameter 1 mm or smaller than 1 mm is drawn by a first thin drawing machine to obtain an Ag—Pd alloy wire with a diameter of 0.5 mm or smaller than 0.5 mm (step 104 c). Then the Ag—Pd alloy wire with a diameter of 0.5 mm or smaller than 0.5 mm is sequentially drawn by the second thin drawing machine (step 104 d), a very thin drawing machine (step 104 e) and an ultra thin drawing machine (step 104 f) to obtain an ultra thin Ag—Pd alloy bonding wire with a predetermined diameter of 0.0508 mm (2.00 mil) to 0.010 mm (0.40 mil).

Step 106, the surface of the Ag—Pd alloy bonding wire is cleaned.

Step 108, the Ag—Pd alloy bonding wire is annealed to ensure a final product with desirable physical properties of breaking load and elongation.

The Ag—Pd alloy bonding wire can be applied to packaging process of IC, LED and SAW because the hardness of the bonding wire is within the range of 60-90 kp/mm2, and the resistance of the bonding wire is within the range of 0.00023-0.00050 ohm, mm2/m.

The invention is more detailed described by three embodiments below:

Embodiment 1

A primary material of Ag is provided and is melted in a vacuum melting furnace. Then, specific amount of a secondary metal material of Pd is added into the vacuum melting furnace, and is co-melted with the primary material in the vacuum melting furnace to obtain an Ag—Pd alloy solution. The Ag—Pd alloy solution consists of: 99.99 wt. % Ag and 0.001 wt. % Pd.

Continuous casting and drawing processes are performed on the Ag—Pd alloy solution to obtain an Ag—Pd alloy wire with a diameter of 4 mm. The Ag—Pd alloy wire is rewired by a reeling machine and then composition analysis is performed on the Ag—Pd alloy wire to check if the obtained composition meets the requirement.

A drawing process is performed on the Ag—Pd alloy wire; the obtained Ag—Pd alloy wire with a diameter of 4 mm is drawn by a first thick drawing machine to obtain an Ag—Pd alloy wire with a diameter of 3 mm. The Ag—Pd alloy wire with a diameter of 3 mm is drawn by a second thick drawing machine to obtain an Ag—Pd alloy wire with a diameter of 1 mm. The Ag—Pd alloy wire with a diameter of 1 mm is drawn by a first thin drawing machine to obtain an Ag—Pd alloy wire with a diameter of 0.18 mm. Then the Ag—Pd alloy wire with a diameter of 0.18 mm is sequentially drawn by the second thin drawing machine, a very thin drawing machine and an ultra thin drawing machine to obtain an ultra thin Ag—Pd alloy bonding wire with a predetermined diameter of 0.050 mm to 0.010 mm.

Finally, the surface of Ag—Pd alloy bonding wire is cleaned and is annealed.

Embodiment 2

A primary material of Ag is provided and is melted in a vacuum melting furnace. Then, specific amount of a secondary metal material of Pd is added into the vacuum melting furnace, and is co-melted with the primary material in the vacuum melting furnace to obtain an Ag—Pd alloy solution. The Ag—Pd alloy solution consists of: 95.00 wt. % Ag and 5.00 wt. % Pd.

Continuous casting and drawing processes are performed on the Ag—Pd alloy solution to obtain an Ag—Pd alloy wire with a diameter of 6 mm. The Ag—Pd alloy wire is rewired by a reeling machine and then composition analysis is performed on the Ag—Pd alloy wire to check if the obtained composition meets the requirement.

A drawing process is performed on the Ag—Pd alloy wire; the obtained Ag—Pd alloy wire with a diameter of 6 mm is drawn by a first thick drawing machine to obtain an Ag—Pd alloy wire with a diameter of 3 mm. The Ag—Pd alloy wire with a diameter of 3 mm is drawn by a second thick drawing machine to obtain an Ag—Pd alloy wire with a diameter of 1.0 mm. The Ag—Pd alloy wire with a diameter of 1.0 mm is drawn by a first thin drawing machine to obtain an Ag—Pd alloy wire with a diameter of 0.18 mm. Then the Ag—Pd alloy wire with a diameter of 0.18 mm is sequentially drawn by the second thin drawing machine, a very thin drawing machine and an ultra thin drawing machine to obtain an ultra thin Ag—Pd alloy bonding wire with a predetermined diameter of 0.050 mm to 0.010 mm.

Finally, the surface of Ag—Pd alloy bonding wire is cleaned and is annealed.

Embodiment 3

A primary material of Ag is provided and is melted in a vacuum melting furnace. Then, specific amount of a secondary metal material of Pd is added into the vacuum melting furnace, and is co-melted with the primary material in the vacuum melting furnace to obtain an Ag—Pd alloy solution. The Ag—Pd alloy solution consists of: 90.00 wt. % Ag and 10.00 wt. % Pd.

Continuous casting and drawing processes are performed on the Ag—Pd solution to obtain an Ag—Pd alloy wire with a diameter of 8 mm. The Ag—Pd alloy wire is rewired by a reeling machine and then composition analysis is performed on the Ag—Pd alloy wire to check if the obtained composition meets the requirement.

A drawing process is performed on the Ag—Pd alloy wire; the obtained Ag—Pd alloy wire with a diameter of 8 mm is drawn by a first thick drawing machine to obtain an Ag—Pd alloy wire with a diameter of 2 mm. The Ag—Pd alloy wire with a diameter of 2 mm is drawn by a second thick drawing machine to obtain an Ag—Pd alloy wire with a diameter of 1.0 mm. The Ag—Pd alloy wire with a diameter of 1.0 mm is drawn by a first thin drawing machine to obtain an Ag—Pd alloy wire with a diameter of 0.18 mm. Then the Ag—Pd alloy wire with a diameter of 0.18 mm is sequentially drawn by the second thin drawing machine, a very thin drawing machine and an ultra thin drawing machine to obtain an ultra thin Ag—Pd alloy bonding wire with a predetermined diameter of 0.050 mm to 0.010 mm.

Finally, the surface of Ag—Pd alloy bonding wire is cleaned and is annealed.

More examples showing the characteristics for the Ag—Pd alloy bonding wire with the diameter of 1.0 mil of the present are listed as below Table 2.

TABLE 2 TYPE DH FH F1H F2H F3H F4H F5H Ag (Wt %) 99.79% 99.45 99.19 99.01 98.15 95.66 92.95 Pd (Wt %) 0.21 0.55 0.81 0.99 1.85 4.34 7.05 Test date 080615 080621 080714 080716 080802 080811 080824 Amount (Kg) 2.395 2.015 3.401 3.030 3.450 3.087 2.861 Draw to V V V V V V V 1.0-0.13 mm Draw to V V V V V V V 0.13-0.05 mm Draw to V V V V V V V 0.05-0.038 mm Draw to V V V V V V V 0.038-0.03 mm Draw to V V V V V V V 0.03-0.025 mm Drawing Test V V V V V V V Break Load (gf) 11.21 12.65 13.11 13.43 13.65 14.37 16.27 Elongation (%) 3.41 3.65 4.12 4.57 5.89 5.83 4.41 Hardness (Hv) 54.8 Hv 57.1 Hv 57.4 Hv 57.8 Hv 58.2 Hv 59.6 Hv 64.5 Hv Resistance (μΩcm) 1.72 1.76 1.84 2.14 2.56 3.50 4.62

Specifically, the F4H bondability and reliability test report is attached for reference.

While the invention is described in by way of examples and in terms of preferred embodiments, it is to be understood that the invention is not limited thereto. On the contrary, the aim is to cover all modifications, alternatives and equivalents falling within the spirit and scope of the invention as defined by the appended claims. 

1. A manufacturing method for a composite alloy bonding wire, comprising: a) providing a primary material of Ag; b) melting the primary material in a vacuum melting furnace, adding a secondary metal material of Pd into the vacuum melting furnace and co-melting with the primary material in the vacuum melting furnace to obtain an Ag—Pd alloy that excludes Mg and Al; c) casting and drawing the Ag—Pd alloy to obtain an Ag—Pd alloy wire; and d) drawing the Ag—Pd alloy wire to obtain an Ag—Pd alloy bonding wire with a predetermined diameter used for packaging processes for IC, LED or SAW.
 2. The manufacturing method according to claim 1, wherein the weight percent of Ag in step a) is 90.00%˜99.99%.
 3. The manufacturing method according to claim 2, wherein the weight percent of Pd in step b) is not more than 10.00 wt. %.
 4. The manufacturing method according to claim 1, wherein the surface of the Ag—Pd alloy bonding wire is cleaned and is annealed after step d).
 5. A alloy bonding wire, comprising: 90.00˜99.99 wt. % Ag; and 0.01˜10.00 wt. % but not more than 10.00 wt. % Pd, wherein the Ag and Pd are melted to obtain an Au—Ag—Pd alloy that excludes Mg and Al, and Ag and Pd are essentially uniformly distributed in the alloy bonding wire, continuous casting and drawing processes are performed on the Ag—Pd alloy to obtain the alloy bonding wire used for packaging processes for IC, LED or SAW. 